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 The arrival of European diseases after Columbus crossed the
Atlantic in 1492 may also have hastened the growth of forests by
killing indigenous people farming the region, the scientists wrote
in the U.S. journal Proceedings of the National Academy of Sciences
(PNAS).
"The dominant ecosystem was more like a savannah than the rainforest
we see today," John Carson, lead author at the University of Reading
in England, said of the findings about the southern Amazon.
The scientists said that a shift toward wetter conditions, perhaps
caused by natural shifts in the Earth’s orbit around the sun, led to
growth of more trees starting about 2,000 years ago.
The scientists studied man-made earthworks, uncovered by recent
logging in Bolivia, that included ditches up to about a kilometer
(1,100 yards) long and up to 3 meters deep and 4 meters wide.
They found large amounts of grass pollen in ancient sediments of
nearby lakes, suggesting the region had been covered by savannah.
They also found evidence of plantings of maize, pointing to farming.
PRISTINE
The Amazon has traditionally been seen as a pristine, dense
rainforest, populated by hunter-gatherers. In recent years, however,
archaeologists have found hints that indigenous peoples lived in the
thick forest, but managed to clear tracts of land for farming.
The PNAS study suggests a new idea – that the forest simply did not
exist in some regions.
The "findings suggest that rather than being rainforest
hunter-gatherers, or large-scale forest clearers, the people of the
Amazon from 2,500 to 500 years ago were farmers," the University of
Reading said in a statement.
Carson said that perhaps a fifth of the Amazon basin, in the south,
may have been savannah until the shift, with forests covering the
rest.
In one lake, Laguna Granja, rainforest plants only took over from
grass as the main sources of pollen in sediments about 500 years
old, suggesting a link to the arrival of Europeans.
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The purpose of the earthworks is unknown - they could have been
defensive or for drainage or religious purposes.
And understanding the forest could help solve puzzles about climate
change.
The Amazon rainforest affects climate change because trees soak up
heat-trapping carbon dioxide as they grow and release it when they
rot or are burnt. Brazil has sharply slowed deforestation rates in
recent years.
Carson said that the growth of Amazonian forests could, for
instance, have contributed to the Little Ice Age, from about 1350 to
1850 by absorbing heat-trapping gases from the air.
Michael Heckenberger, an expert on the Amazon at the University of
Florida, said the study added to evidence that people living in the
Amazon managed nature.
"These indigenous systems were highly sophisticated...There are over
80 domesticated or semi-domesticated crops in the Amazon," he said.
"In Europe at the time they were working with about six."
(Reporting by Alister Doyle; Editing by Lisa Shumaker)
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